Method of making a tubeless tire



April l), i956 R. W. KINDLE ET AL METHOD oF MAKING A TUBELEss TIRE FiledAug. 27, 1953 .AGENT United METHOD or Maroni; A runnrnss rmaVApplication August 27, 195s, sensi No. Smets s claims. (ci. 154-14)This invention relates to an improved pneumatic tire, and moreparticularly it relates to a pneumatic tire of the tubeless typeembodying an air-retaining envelope comprised of a mixture of naturalrubber or butadiene-styrene synthetic rubber and Butyl rubber that hasbeen chemically modied by reaction with dinitrosobenzene, as well as toa method of making such improved tire.

Pneumatic tires of the tubeless type conventionally include an innerlayer or liner of air-retaining material adhered to the band ply of thetire casing, and serving as an impermeable envelope for the air withinthe tire, in place of the usual inner tube. The composition andmanufacture of such a lining material for tubeless tires has up to thepresent time presented a serious dithculty in the manufacture ofsatisfactory tubeless tires, because the materials proposed for thispurpose have all had certain shortcomings, either from the standpoint ofpreparation or'performance, or both. This situation arises because thereare a number of exacting requirements that must be met in a practicaltubeless tire liner, and those skilled in this art have not up to thepresent time been able to work out an entirely satisfactory process andcomposition. No obvious solution to the problem has been forthcomingbecause the lining material, besides being suiiicien'tlyimpermeable toair to permit the tire to be used for reasonable periods withoutrequiring re-inilation, must also have suliicient adhesiveness to remainsecurely united to the inner surface of the tire casing, which isusually made of a composition based mainly on natural rubber or suchsynthetic rubbers as Gli-S. At the same time, it is essential that theliner have good physical properties, so that it does not heat up ordeteriorate in use and so that it does not tend to develop cracks underthe inuence of the repeated severe flexing that it is subjected to inuse. In addition, the liner must have good building tack and form securesplices.

The requirement that the liner stock shall not crack in use has beenparticularly diiiicult to fulfill satisfactorily,

and as a result many premature failures have been noted in conventionalVtubeless tires consequent to the fact that air under pressure passesthrough such cracks from the interior of the tire into the intersticesof the carcass plies, Where it expands under the iniluence of theelevated ternperatures developed in use, thereby' causing separation andfailure of the reinforcing plies. This type of failure commonlymanifests itself as a blowout that occurs suddenly and without warning,to the peril of the occupants ofthe vehicle on which the tire is used.

y art tubeless tires.

Another object of the invention is the provision of a method of making atubeless tire liner material that can tate 2,741,295 Patented Apr. 10,1956 be carried out efficiently and economically in the plant.

The manner in which the invention accomplishes the foregoing objects, asWell as additional objects and advantages, Will be made manifest in thefollowing detailed description, which is intended to be read withreference to the accompanying drawing, the single figure of whichrepresents in transverse cross section a typical tubeless tire made inaccordance With the invention.

The invention contemplates provision of a liner composition for tubelesstires based on the Butyl type of synthetic rubber, that is, a lowtemperature rubbery copolymerizate of an isoolefin such as isobutylenewith a conjugated diolehn such as isoprene or butadiene. Such syntheticelastomers are made by wellknown methods, usually from isoolefins havingfrom 4 to 6 carbon atoms and conjugated diolens having from 4 to 8carbon atoms, the pro-portion of combined dioleiin in the copolymerusually being within the range of from 0.5 to 10%, and more preferablyfrom 0.5 to 5%. Butyl rubber has the advantage of providing the desiredgood air retention, but it cannot be used of itself as a practical linermaterial because it is not compatible with natural rubber or thesynthetic type rubbers used in tire carcasses, and therefore anall-Butyl liner stock has very poor adhesion to the tire carcass stock,or even to the tire fabrics treated with the usual adhesives, that arecommonly based on natural or synthetic rubber latex containing a smallamount of phenol-aldehyde resin.

if it is attempted to render the Butyl rubber adhesive to the tirecarcass by incorporating natural rubber or such synthetic rubbers asGit-S (butadiene-styrene copolymer) with the Butyl, the results areentirely unsatisfactory because of the non-homogeneous nature of such amixture. The incompatibility between the Butyl rubber and the otherrubber manifests itself in extremely poor physical properties, so thatsuch a mixture has no utility. Such blends cannot be successfullyvulcanized because the natural rubber or GR-S rubber in the blendcombines with the available curatives in the mixture.

The present invention is based upon the unexpected discovery that if theButyl rubber is rst modified by reacting it, under critical conditions,with critical, small amounts of dinitrosobenzene, the Butyl rubber isconverted into a condition in which it is apparently readily compatibleWith natural rubber or Gli-S, yielding a blend that is capable ofdeveloping good physical properties upon vulcanization, and that adheresunusually well to the usual tire carcass materials.Para-dinitrosobenzene is the preferred reagent for elfecting the desiredmodification of the Butyl rubber, but meta-dinitrosobenzene may also beused.

in carrying out the invention, the Butyl rubber is masticated at anelevated temperature in the presence of from 0.08 to 0.5 part ofdinitrosobenzene, per parts of the Butyl rubber. Preferably, the amountof dinitrosobenzene employed is from 0.1 to 9.2 part, per 100 parts ofthe Butyl rubber. Such mastication is preferably carried out in thepresence of carbon black, and we preferably employ from about 25 to 75parts of carbon black to 100 parts of Butyl rubber at this stage.Generally, wel mix the carbon black thoroughly with the rubber before weadd the dinitrosobenzene, for the purpose of effecting the requiredchemical modication. With the foregoing amounts of chemical modifyingagents, the desired chemical modification proceeds to the requiredcritical extent when the'mixture is masticatcd for a time ranging from 3minutes at 400 F. to 60 minutes at 300 F., and prefer- @my for 1o yw20minutes t 35o-375 F. n is a charac,-

teristic'of this treatment that the chemical action ofthedim'trosobenzene on the Butyl rubber. is substantially exhausted. Thethus-modified Butyl Vis in no sense a cured or vulcanized material, anditis readily processible, and it is still definitely an unsaturatedmaterial susceptible of vulcanization or cure by the action of suitableadded curatives.

After the modifying step, the batch is usually discharged on a mill andsheeted out. The mix gives a smooth sheet on the mill and can be handledin the same way as a Butyl-carbon black master batch of this type. Nofurther processing or treatment of the Butyl rubber is necfessary.

`The next essential step in the method of the invention is to mix thethus-modified Butyl Vrubber with another type of rubber, preferablycorresponding to the kind of rubber predominating in the tire carcassstock, which is usually either natural rubber (Hevea) or GR-S rubber,

ftheV natural rubberrbeing preferred. The desired physical propertiesareprovided Yby mixing from 40% to 75% (preferably about Sil-60%) of theButyl rubber hydrocarbon with correspondingly from 60% to V25%(preferably about 5 040%) of the other rubber. Before mixing inthe-other rubber, Vsuch other rubber is preferably mixed with additionalcarbon black, usually amounting to from to 75 parts', per 100 parts ofthe other rubber, after which this rubber-carbon black mix is blendedwith the modified Butyl master batch.V The usual processing aids Y andVconventional vulcanizing ingredients are also added to the mix at thispoint. the rubber that is mixed wtih the chemically modified Butyl bethe same rubber as that of the carcass stock, sat- Y not the same. YButyl may be mixed with GR-S in the linen-for applicaisfactory resultsare also obtainable if these rubbers are For example, the chemicallymodified tion to a carcass of natural rubber, or natural rubber may bemixed in the liner to be applied to a GR-S'carcass.

Upon vulcanization of a completed stock of this kind, it is surprisinglyfound that thephysical properties of the vulcanizate far exceed those ofthe Butyl rubber compositions that have heretofore been proposed for useas tube- Although it is preferable that Y less tire liners. Y At thesame time, the air retention proper- Y ties of the stock are excellentand the adhesion of this type of liner compound to carcass stocks andadhesive treated fabrics is superior to the usual Butyl composition.

The following example will serve to illustrate various aspects of theinvention in more detail. In the example all parts are expressed byweight.

Example Referring to the drawing, the invention was employed to make atubeless tire including the usual outer rubber covering 10 constitutingthe tread and sidewall, beneath which there was disposed the usualcarcass 11 composed of a plurality of pliesV of adhesive-treated cordfabric skim* K coated with conventional carcass stock based on naturalrubber. The tire included the usual inextensible bead elements 12 in theends of the carcass, and the under and Vouter portions of the bead areawere provided with a suitable rim sealing material f3 which mayconstitute a continuation of a liner composition 14 applied tothe'interior surfaceV or band ply surface of the carcass in the Y formof a sheet extending from one bead area to the other, in adhesivecontact with theV carcass stock. lf there is no covering of carcassstock on the interior band ply surface,

then the liner 14 is in adhesive contact with the cordsV themselves,bearing the latex-resin adhesive material.

The interior crown surface of the liner preferably has applied thereovera layer V1S of puncture-sealing material,Y

Vthat is capable of sealing any holes accidentally made in the tire byptmcturing objects such as nails. The method of assembling the foregoingparts in their proper relation and Vulcanizing the assembly in thedesired shape in a mold is well understood by those skilledin this art,and

requires no detailed description here. f Y

The liner 14 of the invention was made by rst cornpounding the followingmodified Butyl master batch;

Modified Butyl master batch Ga-r 25 1 150.00V

FEF carbon black 75.00

Polyac 1.00

The polyac was a trade preparation believed to be composed of ,25%para-dinitrosobenzene and of inert material. Therefore, this compositionincluded some 0.16 part of para-dinitrosobenzene per parts of Butyl Yrubber. The GR-I 25 was a commercially -available type of Butyl rubber(copolymer of isobutylene with isoprene), and it was first intimatelymixed with the carbon black in va Banbury mixer, after which thepara-dinitrosobenzene was added and the mixing was continued for 1 5minutes at a temperature range of from 350 F. to 375 F. The batch wasdischarged on a mill and sheeted out to give a smooth sheet. Y r

The following final compound Vwas Ythen prepared, em-

. ploying the foregoing modified Butyl master batch:V

F z'mzl compound 1 Master hatched.

The amount of modified Butyl master batch employed Y coresponds to partsof Butyl rubber hydrocarbon. The compound was mixed with the aid ofa-Banbury mixer (in which the-smoked sheet, carbon-black, oil andstearic acid may first be master hatched) and a roll mill in accordancewith the usual practice in preparing a vulcanizablerubber composition.YThe essential feature of this mixture residesrin the combination of themodified Butyl with the other rubber, in this case natural rubber in theform of smoked sheet, and the remaining compounding ingredients may bevaried at will to provide a typi- Vcal vulcanizablev composition capableof being curedV under the conditions customarily employed iumoldingtires, as will be apparent to the skilled rubber compounder. The mix wasformed into a sheet by calendering, and the liner 1d wasapplied to theinterior of the rawV tire carcass before shaping the same.It'wasobserved that the liner had unusually good tack, and could behandled and applied to the tire carcass with ease. The sheet splicedsatisfactorily, and adhered well to itself as well asto the car-V cass.Thereafter, the'assemblywas shaped and vulcanized in the usual'manner.

Y the liner became permanently adhered to the carcass,

without the aid of any previous special adhesive treatment' or cement.

Samples ofthe liner compound of the invention `after Y i curing in apress for 45 minutes at 45 pounds ofV steam pressure had the followingproperties: Y

remue strength, p. s; i Y1140 Per cent elongation at break 495 Modulusat 300% elongation, p. s. i-.. 590

In contrast to these physical properties, a similar mixture employingButyl rubber reclaim in place of the chemi- In the course of thevulcanization,

cally modified Butyl rubber employed in the composition of the inventionhad the following physical properties:

Tensile, p. s. i 580 Per cent elongation at break 590 Modulus at 300%elongation, p. s. i 215 The superiority of the liner of the inventionwill be apparent from a comparison of the two foregoing sets of physicalproperties.

in order to further demonstrate the superiority of the liner of thepresent invention, a number of tires were made up with liners similar tothat described in the foregoing working example. The tires were mountedand inated to a denite standard pressure and subjected to a standardload, While running against a cleated test Wheel at a definite speed.Under the conditions of the test, the tires made in accordance with theinvention ran for an average of 95.8 hours Without failure. Undersimilar conditions, tubeless tires with liners made of a similarcomposition, but based on Butyl inner tube reclaim, instead of onchemically modied butyl rubber in accordance With the invention, ran foran average of only 51 hours before failure. As can be seen from thisdata, our invention has therefore definitely improved the quality of thetire. In addition to the improved life, the tires embodying the liner ofthe invention had very little cracking in the liner stock as compared tothe liner based on reclaim Butyl, which were exceptionally badlycracked.

The improvement realized with the liner composition of the invention isbelieved to be due at least in part to the fact that the chemicaltreatment of the Butyl rubber under the critical conditions employed inthe invention does not result in any powerful residual accelerating orcuring material being present in the Butyl. In any event, Butyl reclaim,or any Butyl rubber that has first been substantially cured with theusual vulcanizing agents and accelerators, and thereafter refined toapproximate a reclaim, is not capable of providing a liner compositionthat at once has good splicing qualities and does not crack in use,While being singularly immune to progressive deterioration andundesirable change in physical properties, as the liner compositionsmade in accordance with the invention are.

Having thus described our invention, what we claim and desire to protectby Letters Patent is:

1. A method of making a tubeless tire comprising in combination thesteps of chemically modifying a rubbery copolymer of an isoolen havingfrom 4 to 6 carbon atoms with from 0.5 to of a conjugated diolen havingfrom 4 to 8 carbon atoms by masticating 100 parts of said rubberycopolymer with from 0.08 to 0.5 part of dinitrosobenzene for from 3minutes at 400 F. to 60 minutes at 300 F., to yield an essentiallyuncured, processible, lsheetforming, unsaturated, vulcanizablc material,mixing from 40 to 75% by Weight of the thus-modified copolymer withcorrespondingly from 60 to 25 of a rubber selected from the groupconsisting of natural rubber and butadienestyrene copolymer rubber,compounding the mixture with vulcanizing agents, applying the resultingcomposition to the interior of a tire casing having a carcass comprisingcord fabric coated with a vulcanizable rubber composition selected fromthe group consisting of natural rubber and butadiene-styrene copolymerrubber compositions, and thereafter vulcanizing the assembly in tireshape.

2. A method of making a tubeless tire comprising in combination thesteps of chemically modifying a rubbery copolymer of an isooleiin havingfrom 4 to 6 carbon atoms with from 0.5 to 10% of a conjugated diolenhaving from 4 to 8 carbon atoms by masticatng 100 parts of said rubbercopolymer with from 0.08 to 0.5 part of paradinitrosobenzene for from 3minutes at 400 F. to 60 minutes at 300 F., to yield an essentiallyuncured, processible, sheet-forming, unsaturated, Vulcanizable material,

mixing from 40 to 75% by weight of the thus-modified copolymer withcorrespondingly from 60 to 25% of a rubber selected from the groupconsisting of natural rubber and butadiene-styrene copolymer rubber,compounding the mixture with vulcanizing agents, applying the resultingcomposition to the interior of a tire casing having a carcass comprisingcord fabric coated with a vulcanizable rubber composition selected fromthe group consisting of natural rubber and butadiene-styrene copolymerrubber compositoins, and thereafter vulcanizing the assembly in tireshape.

3. A method of making a tubeless tire comprising in combination thesteps of chemically modifying a rubbery copolymer of isobutylene withfrom 0.5 to 5% of isoprene by mastcating parts of said rubbery copolymerwith from 0.1 to 0.2 part of para-dinitrosobenzene for from 10 to 20minutes at from 350 to 375 F., to yield an essentially uncured,processible, sheet-forming, unsaturated, vulcanizable material, mixingfrom 40 to 75% by Weight of the thus-modified copolymer withcorrespondingly from 60 to 25% of a rubber selected from the groupconsisting of natural rubber and butadiene-stryrene copolymer rubber,compounding the mixture with vulcanizing agents, applying the resultingcomposition to the interior of a tire casing having a carcass comprisingcord fabric coated with a vulcanizable rubber selected composition fromthe group consisting of natural rubber and butadienestyrene copolymerrubber compositionaand thereafter vulcanizing the assembly in tireshape.

4. A method of making a tubeless tire comprising in combination thesteps of chemically modifying a rubbery copolymer of isobutylene withfrom 0.5 to 5% of isoprene by masticating 100 parts of said rubberycopolymer with from 0.1 to 0.2 part of para-dinitrosobenzene for from l0to 20 minutes at from 350 to 375 F., to yield an essentially uncured,processible, sheet-forming, unsaturated, Vulcanizable material, mixingfrom 40 to 75% by Weight of the thus-modified copolymer withcorrespondingly from 60 to 25% of natural rubber, compounding themixture with vulcanizing agents, applying the resulting composition tothe interior of a tire casing having a carcass comprising cord fabriccoated with a vulcanizable natural rubber composition, and thereaftervulcanizing the assembly in tire shape.

5. A method of making a tubeless tire comprising in combination thesteps of chemically modifying a rubbery copolymer of isobutylene withfrom 0.5 to 5% of isoprene by masticating 100 parts of said rubberycopolymer with from 0.1 to 0.2 part of para-dim'trosobenzene for from 10to 20 minutes at from 350 to 375 F., to yield an essentially uncured,processible, sheet-forming, unsaturated, vulcanizable material, mixingfrom 50 to 60% by Weight of the thus-modified copolymer withcorrespondingly from 50 to 40% of natural rubber, compounding themixture with vulcanizing agents, applying the resulting composition tothe interior of a tire casing having a carcass comprising cord fabriccoated with a vulcanizable natural rubber composition, and thereaftervulcanizing the assembly in tire shape.

References Cited in the file of this patent UNITED STATES PATENTS2,526,504 Renner, Jr., et al Oct. 17, 1950 2,541,550 Sarbach et al. Feb.13, 1951 2,566,384 Tilton, lr. Sept. 4, 1951 2,575,249 Connell et al.Nov. 13, 1951 2,583,387 Morrissey et al. Jan. 22, 1952 2,616,876 Renner,Jr., et al. Nov. 4, 1952 2,625,523 Garber et al Ian. 13, 1953 2,676,636Sarbach Apr. 27, 1954 2,698,042 Perkins Dec. 28, `1954

1. A METHOD OF MAKING A TUBELESS TIRE COMPRISING IN COMBINATION THESTEPS OF CHEMICALLY MODIFYING A RUBBERY COPOLYMER OF AN ISOOLEFIN HAVINGFROM 4 TO 6 CARBON ATOMS WITH FROM 0.5 TO 10% OF A CONJUGATED DIOLEFINHAVING FROM 4 TO 8 CARBON ATOMS BY MASTICATING 100 PARTS OF SAID RUBBERYCOPOLYMER WITH FROM 0.08 TO 0.05 PART OF SAID RUBBENZENE FOR FROM 3MINUTES AT 400*F. TO 60 MINUTES AT 300*F., TO YIELD AND ESSENTIALLYUNCURED, PROCESSIBLE, SHEETFORMING, UNSATURATED, VULCANIZABLE MATERIAL,MIXING FROM 40 TO 75% BY WEIGHT OF THE THUS-MODIFIED COPOLYMER WITH